This invention generally relates to electrical generators and, more particularly, to means for supporting stator windings in superconductive generators.
In a conventional turbine generator the conductors in the stator winding are embedded in slots located in an iron yoke. The slots in the yoke form a plurality of iron teeth that effectively shield the stator windings from the radial magnetic field generated by the rotor. The stator windings are thereby not subjected to torsional forces and are rigidly supported during operation of the generator.
In contrast, in a superconductive electrical generator the stator windings are usually not located in slots in an iron yoke but are located in the air-gap between the yoke and the rotor. The magnetic flux density in a superconductive generator is generally so high that any iron teeth located near the rotor become saturated. When saturation occurs, the iron teeth cause large electrical losses and become very difficult to cool.
Although an air-gap stator winding solves the problem of saturation of the yoke, an air-gap winding is inherently subject to both transverse and radial magnetic fields. These two fields cause both stresses and torques on the windings. Further, air-gap windings are subjected to high flux densities which can cause substantial eddycurrent losses as well as large circulating current losses.
One prior approach to the support of stator windings in the air-gap of a superconductive generator has been to subdivide the individual conductors in the winding into small strands and to wedge the individual strands into place around the inside of the yoke. Integral stator bars are not formed and the conductors are both insulated and cooled with oil.
Another approach has been to wire the stator winding in the machine by hand and then to impregnate all of the conductors together with an epoxy resin. The entire assembly is thereby rigidly secured in place to form a single integral module.
These prior approaches are typically operated at low current levels and without generating much stress on the conductors. In addition, these prior machines do not use a stator bar construction that permits a portion of the stator winding to be removed for repair in the event of failure.
Thus, there has been a continuing need to develop a high-strength stator winding that can be subjected to high levels of stress and torque. Since it is now contemplated that superconductive generators can have an output of 1200 thousand KVA or more, the stators therein must be capable of withstanding the tremendous forces generated during a three-phase short-circuit across the output terminals.